Accurate speed measurement can be important for mobile machines. For example, speed measurement can be used as input for traction control systems, guidance systems, braking systems, navigation systems, and many other machine systems. If a detected speed is not accurate, performance and/or stability of the related system could be negatively affected.
Many different types of sensors can be used for speed measurement purposes. For example, an onboard navigation receiver may interface with a local laser or global satellite transmitter and determine a change in position of the machine within a prescribed period of time based on a received signal, the change in position then being used together with the period of time to calculate travel speed. A Doppler sensor may use radio waves to detect distance changes from a receiver onboard the machine to objects in an environment surrounding the machine, the distance changes then being used together with an elapsed period of time to calculate a travel speed. Cameras may similarly be used to detect changes in size and or location of images of objects in the machines environment and thereby calculate the travel speed. Magnetic and/or optical sensors may be used to detect a rotational speed of a machine component (e.g., an axle, a gear, or a wheel), the rotational speed then being used along with known kinematics of the machine to calculate the travel speed. Other ways of detecting a machine speed may also be possible.
One problem associated with each of the sensors described above, and other sensors known in the art, involves angular acceleration (e.g., pitching) of the mobile machine in a direction aligned with rotation being measured. For example, during travel of a machine, the part of the machine on which the speed measurement sensor is mounted could pitch forward or backward. When this happens, the speed measurement sensor does not recognize that the machine is pitching, and will erroneously include the pitch rate as a change in speed of the machine component (e.g., the wheel). For example, when pitching forward, the speed measurement sensor will artificially deflate the travel speed of the machine because of the pitching. Likewise, when pitching rearward, the speed measurement sensor will unknowingly inflate the speed of the machine component. When other machine systems use these deflated or inflated speed values, the machine may react in unpredictable and/or undesired ways.
One attempt to improve machine control is disclosed in U.S. Pat. No. 8,600,621 of Callaway et al. that issued on Dec. 3, 2013 (“the '621 patent”). Specifically, the '621 patent discloses a traction control system for a mobile machine. The system includes a first sensor that indicates a speed of a wheel of the machine, a second sensor that indicates an acceleration of the machine, and a third sensor that indicates a pitch rate of the machine. The first sensor is a magnetic sensor located on a hydraulic motor used to drive the wheel. The second sensor is a 3-axis accelerometer. The third sensor is a gyroscope. A controller determines a drive acceleration by differentiating a signal from the first sensor, and determines a ground acceleration based on a signal from the second sensor. The controller adjusts the ground acceleration based on differentiation of a signal from the third sensor to account for machine pitching. The controller then selectively activates a traction control algorithm based on a difference between the drive acceleration and the adjusted ground acceleration.
While the system of the '621 patent may be helpful in many applications to control wheel slip, it may still be less than optimal in other applications. For example, the controller may not be able to determine if the speed signal from the first sensor is accurate. That is, the speed sensor could be producing an erroneous speed signal due to pitching of the machine (and the speed sensor itself), and the controller of the '621 patent could be unaware of the situation.
The present disclosure is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.